In typical computer- or machine-aided applications, a considerable proportion of the computer operations relates to the transfer of data between an internal memory and external peripheral units or modules. A simple example is the loading of data from an external data memory into the main memory of a computer, so that the processor referred to as central processing unit (CPU) can access these data and process them. In reverse, it is frequently necessary to transfer the data stored at different memory locations to various input/output devices or to write data into the memory from these input/output devices. To relieve the processor of the task of data transfer, DMA controllers are often used for this. If the processor ascertains that an input or output of data is required, relevant commands are transmitted by the processor to the DMA controller, wherein these commands may comprise in particular the address of the data to be transferred, the volume of the data to be transferred and the destination of the data transfer. The DMA controller then carries out the data transfer on the basis of these commands, wherein the processor can in the meantime continue with other operations until an interrupt generated by the DMA controller indicates the end of the data transfer. In this way, an appreciable amount of time can be saved owing to the support of the DMA controller.
DMA controllers are also used in systems with broadband access, in particular with DSL access. Conventionally a modem is used for internet access in home applications with broadband access, wherein an even data stream is transferred. The DMA controllers used in conventional broadband systems here transfer the data from various peripheral units (e.g., bus adapter, DSL line, Ethernet switch, etc.) to the memory of the system (i.e., in the receiving direction) and from the memory to the various peripheral units (i.e., in the sending direction) according to a simple “round robin” algorithm, without quality of service (QoS) being supported, even if the peripheral units themselves may possibly support QoS. This data transfer mechanism is adequate for purely data applications, though future needs in broadband systems in particular for home applications may possibly not be met by this.
Modern hardware components for wide area network (WAN) networks (e.g., gateways, routers, DSLAMs, etc.) are normally capable of supporting QoS for different data streams, without, however, QoS so far being fully implemented into the hardware of modems for broadband access. There are different reasons for this, one reason being in particular that the market for home applications with broadband access is subject to extreme price pressure.
Nevertheless, it is still desirable that every component involved in a data transfer in the different network systems is capable of effectively supporting QoS, in order to keep the overall delay time fluctuations, also known as “jitters,” to a minimum. This desire to minimize jitters will increase as the need for transfer of both voice information and items of video information and data streams via the internet using a broadband access continually increases, in particular for home applications.